ROME, Italy (CNN) -- Two controversial world leaders known for their anti-western rhetoric took advantage of a U.N. summit to point the finger of blame for the current food crisis at western nations.

Iranian President Mahmoud Ahmadinejad and Zimbabwe's Robert Mugabe used the platform of a food summit in Rome to condemn western policies on the issue.

Ahmadinejad suggested the formation of a global organization to regulate the food market and listed the major factors that he believes are behind the current high food prices.

"The devaluation of the dollar and the global inflation, and some others consider environmental changes and droughts, the increase in consumption, the inappropriateness of agricultural methods and the low level of production efficiency, and the witness of farmers," he said.

As a solution, the Iranian president suggested "the formation of an independent and powerful body, obeyed by all countries, to justly regulate the food market and organize all its related issues from production to consumption."

The Zimbabwean leader was more pointed in his attack, however, singling out Britain as the cause of the economic woes back in his homeland.

Zimbabwe has suffered a dramatic drop in food production and agricultural exports in recent years: The country once known as southern Africa's "breadbasket" is now among a list of 22 countries identified by the U.N. as particularly at risk of food shortages.

Many critics blame Mugabe's policies for the turnaround, especially his controversial land reform programs, which redistributed large farms that had been held by about 4,000 white landowners to formerly landless families.

Mugabe was unrepentant, however, telling the U.N. summit that Zimbabweans had "welcomed" the land reform program.

He said that in "retaliation" for the land reforms, Britain had persuaded other Western powers to impose policies against Zimbabwe that "cripple" his country's economy and "thereby effect illegal regime change."

The Zimbabwean leader, whose presence at the three-day U.N. food summit is causing outrage among some leaders, said Britain "mobilized" allies in Europe, North America and elsewhere to impose "illegal economic sanctions" against Zimbabwe and to cut off "all developmental assistance."

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Earlier at the Rome summit, U.N. chief Ban Ki-Moon called for a drastic increase in food production to meet the demands of a rising population and stave off a crisis brought about by oil prices, climate change and the impact of the biofuel market.

Ban, speaking at the opening of the event, said production must take urgent measures to feed 862 million hungry people worldwide and ensure security for the global population.

"Hundreds of millions of the world's people expect no less," Ban said.

"Nothing is more degrading than hunger, especially when it is man-made. It breeds anger, social disintegration, ill health and economic decline. In the name of the development goals we all set at the millennium, the right to food and our common humanity, I urge all of you to act together now."

Ban said countries must also expand microcredit to small farmers, minimize trade barriers and tariffs, and boost investment in agriculture.

Countries must reach a consensus on the production of biofuels -- one of the many causes of rising food prices -- and reduce subsidies to those that produce it, Ban said.

With the world's population expected to grow to 7.2 billion by 2016, Ban said, the food problem will only grow if the world doesn't act now.

The head of the U.N. Food and Agriculture Organization, which is hosting the conference, appealed to world leaders for $30 billion a year to "relaunch agriculture" and avert future threats to conflicts over food.

The solution, FAO Director-General Jacques Diouf said, is increasing production and productivity in the low-income, food-deficit countries.

He said the world food crisis has had "tragic political and social consequences" in some countries and could further endanger world security.

"Important today is to realize that the time for talking is long past," Diouf said. "Now is the time for action."

Diouf noted that nearly a decade ago, more than 100 countries attending the World Food Summit pledged to halve world hunger by 2015. But despite that 1996 pledge, Diouf said, resources to finance agricultural programs in developing countries have not only failed to grow but have decreased significantly.

Leaders at the summit will be discussing how to sustain emergency deliveries of food when the cost of agricultural products -- and the fuel necessary to produce and distribute them -- is skyrocketing.

Saudi Arabia is giving about $500 million to the World Food Program to deal with the emergency in the short term, but experts say longer-term solutions, like investing in agricultural development, are just as critical.

The United States has committed $5 billion over the next two years, much of it to help find long-term solutions.

U.S. President Bush condemned Mugabe's presence at the event in a statement released Tuesday.

"While Robert Mugabe makes political statements in Rome, his people continue to face empty markets at home," Bush said in the statement. "The United States currently feeds more than 1 million Zimbabweans and spent more than $170 million on food assistance in Zimbabwe last year. We will continue these efforts to prevent government-induced starvation in Zimbabwe."

Britain's international development secretary, Douglas Alexander, said in Rome that Mugabe has "neither the credibility or the authority" to speak about food prices or food production.

"I regard the attendance of Robert Mugabe at this summit as, quite frankly, obscene," Alexander said. "This is a man who has impoverished his country."

Mugabe, who is facing a fierce reelection battle with opposition challenger Morgan Tsvangirai this month, is banned from traveling to the European Union but received special permission to attend the U.N.-organized event.